(based on today's contract prices)
2019: Wisconsin, USC, Washington, Boise St.
2020: Michigan St., Missouri, Utah St.
2021: Arizona (in Las Vegas, but part of BYU tv rights), ASU, Boise St.
If BYU can continue to go bowling each season, when the ESPN contract is up, it will be renewed or replaced for at least twice the current contract price.
Note also that BYU signed its ESPN TV deal a year or two before the Big 12, PAC 12, and SEC signed their massive TV deals. So, timing wasn't great for BYU's current contract, and there were an awful lot of WAC games on the BYU schedule - just to make independence work in the short term.